Control device for internal combustion engine

ABSTRACT

The invention relates to a control device applied to a cylinder injection type of an internal combustion engine ( 10 ). The control device control a disperse parameter for changing a degree of a spread of the fuel spray injected from the injector ( 20 ) such that the maximum degree of the spread of the fuel spray under a state where an amount of the fuel adhering to the spark generation part ( 31   a ) of the spark plug ( 30 ) at the ignition timing corresponds to a first amount, is smaller than the maximum degree of the spread of the fuel spray under a state where the amount of the fuel adhering to the spark generation part at the ignition timing corresponds to a second amount smaller than said first amount.

TECHNICAL FIELD

This invention relates to a control device for a cylinder injection typeof an internal combustion engine comprising an injector (an in-cylinderfuel injector for injecting a fuel directly into a cylinder (acombustion chamber).

BACKGROUND ART

One of the conventionally known cylinder injection type of the internalcombustion engine comprises fuel injectors and spark plugs. Each of theinjector has at least one injection hole exposing to the interior of thecombustion chamber. Each of the spark plug has a spark generation part(an electrode part) exposing to the interior of the combustion chamber.In one of such engines, the injector and the corresponding spark plugare positioned such that the fuel (actually, the fuel spray) injectedfrom the injector reaches the spark generation part of the spark plugdirectly (for example, refer to the Patent Literature 1). Thereby, themixture gas having a high ignition property can be formed around thespark generation part and can be ignited. As a result, the amount of theinjected fuel can be reduced and thus, the fuel consumption can beimproved. Such an engine is also referred to as “a spray guided type ofthe internal combustion engine” because the fuel spray is introduced(guided) directly to the spark generation part by the fuel injection.

CITATION LIST Patent Literature

-   [PTL. 1]

JP 2008-31930 A

SUMMARY OF INVENTION

In the spray guided type of the engine, because the fuel spray reachesthe spark generation part of the spark plug directly, the spark is oftengenerated under a state where the fuel adheres to the spark generationpart and as a result, the smolder of the spark plug occurs.

The invention is made to solve the problem described above. That is, oneof the objects of the invention is to provide a control device of aninternal combustion engine, applied to a spray guided type of the enginein which the fast increasing of the smolder of the spark plug isprevented. Hereinafter, the control device according to the inventionwill be referred to as “the invention device”.

The internal combustion engine (the cylinder injection type of theinternal combustion engine) which the invention device is applied to,comprises a spark plug having a spark generation part (an electrodepart) and an injector (an in-cylinder fuel injector) having a movablevalve body and at least one injection hole.

The injector injects a fuel from the injection hole directly into acylinder (a combustion chamber) of the engine by moving the valve body.Further, the injector is positioned and configured such that the fuelspray including at least a part of the fuel injected from the injectorreaches the spark generation part of the spark plug directly.

Further, the invention device comprises a control part. The control partis configured to:

execute the fuel injection by the injector; and

generate a spark for the ignition of the fuel from the spark generationpart at a predetermined ignition timing.

Furthermore, the control part is configured to control a disperseparameter for changing (adjusting) the maximum degree of the spread ofthe fuel spray such that the maximum degree of the spread of the fuelspray under a state Where the amount of the fuel adhering to the sparkgeneration part at the ignition timing corresponds to a first amount, issmaller than the maximum degree of the spread of the fuel spray under astate where the amount of the fuel adhering to the spark generation partat the ignition timing corresponds to a second amount smaller than thefirst amount. It should be noted that the first and second amounts arenot predetermined fixed amounts, but are relative amounts.

The degree of the spread of the fuel spray means the degree of thedisperse of the fuel spray, the fuel spray angle (the angle of thespread of the fuel spray), the amount of the fuel spray from theinjection hole toward the spark generation part, etc. In other words, asthe degree of the spread of the fuel spray increases, the degree of thedisperse of the fuel spray and the fuel spray angle increase. Further,it can be said that the injector (and the injection hole) and the sparkgeneration part are positioned relative to each other such that theamount of the fuel spray from the injection hole toward the sparkgeneration part increases as the degree of the spread of the fuel sprayincreases. That is, for example, the spark plug and the injector arepositioned and configured such that the spark generation part is locatedbetween the fuel sprays each formed by the fuel injected from each oftwo adjacent injection holes.

Thereby, when the amount of the fuel adhering to the spark generationpart at the ignition timing immediately before the ignition timing) islarge (that is, for example, when the temperature of the sparkgeneration part is low and thus, the smolder of the spark plug easilyoccurs due to the ignition of the fuel), the disperse parameter iscontrolled at a value which decreases the maximum degree of the spreadof the fuel spray, compared with the maximum degree of the spread of thefuel spray when the amount of the fuel adhering to the spark generationpart at the ignition timing is small. Therefore, the excessiveincreasing of the degree of the spread of the fuel spray is preventedand thus, the excessive increasing of the amount of the fuel adhering tothe spark generation part is prevented. As a result, the fast increasingof the smolder of the spark plug can be prevented.

According to one aspect of the invention device, the control part isconfigured to use a maximum value of the lift amount of the valve body(that is, the moving amount of the valve body) in the fuel injection asthe disperse parameter. Further, the control part is configured todecrease the maximum degree of the spread of the fuel spray by changingthe lower limit of the maximum value of the lift amount in a precedinginjection Which is carried out immediately before the ignition timingsuch that the lower limit under a state where the adhering fuel amountcorresponds to a first amount, is larger than the lower limit under astate where the adhering fuel amount corresponds to a second amount.

As the maximum value of the lift amount of the valve body of theinjector in the fuel injection decreases, the penetration force of theinjected fuel weakens and the degree of the spread of the fuel sprayincreases. Therefore, as in the aspect described above, the excessiveincreasing of the degree of the spread of the fuel spray is prevented bymaking the lower limit of the maximum value of the lift amount under astate where the amount of the fuel adhering to the spark generation partis large, larger than the lower limit of the maximum value of the liftamount under a state where the amount of the fuel adhering to the sparkgeneration part is small. Thereby, the adhering of the excessive largeamount of the fuel to the spark generation part can be prevented whenthe amount of the fuel adhering to the spark generation part is likelyto increase. As a result, the fast increasing of the degree of thesmolder of the spark plug can be prevented.

In this case, the control part may be configured to change the lowerlimit on the basis of the temperature of the spark generation part inconsideration of the fact that the fuel adhering amount corresponds tothe first amount when the temperature of the spark generation partcorresponds to a first temperature while the fuel adhering amountcorresponds to the second amount when the temperature of the sparkgeneration part corresponds to a second temperature higher than thefirst temperature.

Thereby, as the temperature of the spark generation part lowers (thatis, as the amount of the fuel adhering to the spark generation partincreases), the lower limit of the maximum value of the lift amountincreases. As a result, the adhering of the excessive large amount ofthe fuel to the spark generation part due to the excessive increasing ofthe degree of the spread of the fuel spray, can be prevented and thus,the fast increasing of the degree of the smolder of the spark plug canbe prevented.

Further, in this case, the control part may be configured to acquire thetemperature of the spark generation part on the basis of the coolingwater temperature (the temperature of the cooling water of the engine).The cooling water temperature has a strong correlation with thetemperature of the engine and thus, the cooling water temperature alsohas a strong correlation with the temperature of the spark generationpart of the spark plug. In particular, when the engine operation starts,the temperature of the spark generation part has an extremely strongcorrelation with the cooling water temperature. Therefore, as in theconfiguration described above, the adhering of the excessive largeamount of the fuel to the spark generation part can be prevented by asimple configuration by changing the lower limit of the maximum value ofthe lift amount of the valve body on the basis of the cooling watertemperature. As a result, the fast increasing of the degree of thesmolder of the spark plug can be prevented.

It should be noted that the control part may be configured to use thecooling water temperature as the temperature of the spark generationpart, in particular when the engine operation starts or immediatelyafter the engine operation stalls. Further, the control part may beconfigured to estimate the temperature of the spark generation part onthe basis of the cooling water temperature at the engine operation startand the sum of the number of the ignition operation after the engineoperation start or the sum of the estimated value of the temperatureincrease at the spark generation part derived from one combustion afterthe engine operation start.

Further, the control part may be configured to change the lower limit onthe basis of the fuel pressure at the timing of carrying out thepreceding injection in consideration of the fact that the fuel adheringamount corresponds to the first amount under a state where the fuelpressure at the timing of carrying out the preceding injectioncorresponds to a first pressure while the fuel adhering amountcorresponds to the second value under a state where the fuel pressure atthe timing of carrying out the preceding injection corresponds to asecond pressure lower than the first pressure.

As the fuel pressure at the timing of carrying out the precedinginjection increases, the strength of the turbulence of the flow of thefuel flowing into the injection hole from the fuel passage of theinjector increases and thus, the degree of the spread of the fuel sprayincreases. Accordingly, as in the configuration described above, theadhering of the excessive large amount of the fuel to the sparkgeneration part due to the excessive increasing of the degree of thespread of the fuel spray can be prevented by changing the lower limit onthe basis of the fuel pressure (that is, by increasing the lower limitas the fuel pressure increases). As a result, the fast increasing of thedegree of the smolder of the spark plug can be prevented. It should benoted that for example, the control part may be configured to correctthe lower limit, which has been changed on the basis of the temperatureof the spark generation part, on the basis of the fuel pressure suchthat the lower limit increases as the fuel pressure at the timing ofcarrying out the preceding injection increases.

Further, as the amount of the fuel injected by the preceding injectionincreases, the amount of the fuel reaching and adhering to the sparkgeneration part increases. Accordingly, the control part may beconfigured to change the lower limit on the basis of the fuel injectionamount of the preceding injection in consideration of the fact that thefuel adhering amount corresponds to the first amount under a state wherethe fuel injection amount of the preceding injection corresponds to afirst injection amount while the fuel adhering amount corresponds to thesecond amount under a state where the fuel injection amount of thepreceding injection corresponds to a second injection amount smallerthan the first injection amount. Thereby, the adhering of the excessivelarge amount of the fuel to the spark generation part can be prevented.As a result, the fast increasing of the degree of the smolder of thespark plug can be prevented. It should be noted that for example, thecontrol part may be configured to correct the lower limit, which hasbeen changed on the basis of the temperature of the spark generationpart or corrected on the basis of the fuel pressure, on the basis of thefuel injection amount of the preceding injection such that the lowerlimit increases as the fuel injection amount of the preceding injectionincreases.

In addition, the control part may be configured to:

acquire a first parameter expressing the degree of the smolder of thespark generation part; and

change the lower limit such that the lower limit increases as the degreeof the smolder expressed by the acquired first parameter increases.

The first parameter can be easily acquired by measuring the dielectricbreakdown voltage at the timing of carrying out the ignition, theinsulation resistance of the spark generation part, etc. According tothe configuration described above, the lower limit is changed such thatthe lower limit increases as the degree of the smolder expressed by thefirst parameter increases. Therefore, as the degree of the smolder ofthe spark plug increases, the maximum degree of the spread of the fuelspray can be decreased and thus, the amount of the fuel adhering to thespark generation part can be decreased and the fast increasing of thedegree of the smolder can be prevented. It should be noted that forexample, the control part may be configured to correct the lower limit,which has been changed on the basis of the temperature of the sparkgeneration part or corrected on the basis of the fuel pressure and/orthe fuel injection amount, on the basis of the first parameter such thatthe lower limit increases as the degree of the smolder expressed by thefirst parameter increases.

The injector may have a sac chamber in the tip end of the injector, thesac chamber communicating with the injection hole under a state Where atleast the valve body is moved. Further, the control part may beconfigured to execute a fuel injection as a pre-injection in addition tothe preceding injection by the injector at a timing before the precedinginjection.

When the pre-injection is carried out, in some cases, the flow of thefuel occurs in the sac chamber and the flow of the fuel remains (is notreduced) at the timing of carrying out the preceding injection. Forconvenience, the fuel flow generated by the pre-injection and remainingin the sac chamber at the injection start timing of the precedinginjection will be referred to as “the sac chamber fuel flow”. When thepreceding injection is carried out under a state where the sac chamberfuel flow occurs, the injected fuel is subject to the influence of thesac chamber fuel flow and thus, the degree of the spread of the fuelspray increases. As a result, the amount of the fuel adhering to thespark generation part increases and thus, the fast increasing of thedegree of the smolder of the spark plug may occur.

Accordingly, the control part is configured to:

acquire a second parameter having a correlation with the strength of thesac chamber fuel flow; and

change the lower limit such that the lower limit increases as thestrength of the sac chamber fuel flow expressed by the acquired secondparameter increases.

Thereby, as the strength of the sac chamber fuel flow expressed by thesecond parameter increases, the lower limit increases. Therefore, evenwhen the strength of the sac chamber fuel flow is large, the excessiveincreasing of the degree of the spread of the fuel spray is preventedand thus, the adhering of the excessive large amount of the fuel to thespark generation part can be prevented. As a result, the fast increasingof the degree of the smolder of the spark plug can be prevented.

The control part may be configured to acquire the second parameter onthe basis of the time period between the injection end timing of thepre-injection and the injection start timing of the preceding injection.For convenience, hereinafter, the time period may be referred to as “theinterval with respect to the pre-injection”. The reason for using theinterval with respect to the pre-injection to acquire the secondparameter is because the strength of the sac chamber fuel flow increasesas the interval with respect to the pre-injection shortens. In thiscase, the control part may be configured to use the interval withrespect to the pre-injection as the second parameter or acquire thesecond parameter on the basis of the interval with respect to thepre-injection and the other parameter(s) (for example, a fuel injectionamount of the pre-injection described below).

Alternatively, the control part may be configured to acquire the secondparameter on the basis of the fuel injection amount of thepre-injection. This is because the strength of the sac chamber fuel flowincreases as the fuel injection amount of the pre-injection increases.In this case, the control part may be configured to use the fuelinjection amount of the pre-injection as the second parameter or acquirethe second parameter on the basis of the fuel injection amount of thepre-injection and the other parameter(s) (for example, the maximum valueof the lift amount of the valve body in the pre-injection and the fuelpressure at the timing of carrying out the pre-injection).

Alternatively, the control part may be configured to acquire at leastone of the pressure of the fuel in the sac chamber during the timeperiod between the injection end timing of the pre-injection and theinjection start timing of the preceding injection and the pressure ofthe fuel upstream of the seat part where the valve body abuts the edgepart of the injection hole in the fuel injector during the time periodbetween the injection end timing of the pre-injection and the injectionstart timing of the preceding injection.

That is, the control part may be configured to estimate (acquire) thestrength of the sac chamber fuel flow directly on the basis of thechange of the pressure of the fuel in the injector.

According to the other aspect of the invention device, the control partis configured to use the time period between the injection end timing ofthe pre-injection and the injection start timing of the precedinginjection (the interval with respect to the pre-injection) as thedisperse parameter. Then, the control part is configured to decrease themaximum degree of the spread of the fuel spray by changing the minimumvalue of the time period described above (the interval with respect tothe pre-injection) such that the minimum value of the time period undera state where the fuel adhering amount corresponds to the first amount,is larger (longer) than the minimum value of the time period under astate where the fuel adhering amount corresponds to the second amount.That is, when the amount of the fuel adhering to the spark generationpart is large, the minimum value of the time period between theinjection end timing of the pre-injection and the injection start timingof the preceding injection (the interval with respect to thepre-injection) elongates.

As the interval with respect to the pre-injection is small (short), thesac chamber fuel flow is strong and thus, the fuel injected by thepreceding injection is strongly subject to the influence of the sacchamber fuel flow. As a result, the degree of the spread of the fuelspray increases. Therefore, as in the aspect described above, even whenthe amount of the fuel adhering to the spark generation part increases,the excessive increasing of the degree of the spread of the fuel spraycan be prevented and thus, the adhering of the excessive large amount ofthe fuel to the spark generation part can be prevented by changing theminimum value of the interval with respect to the pre-injection suchthat the minimum value of the interval with respect to the pre-injectionunder a state where the amount of the fuel adhering to the sparkgeneration part is large, is larger than the minimum value of theinterval with respect to the pre-injection such that the minimum valueof the interval with respect to the pre-injection under a state wherethe amount of the fuel adhering to the spark generation part is small.As a result, according to the aspect described above, the fastincreasing of the degree of the smolder of the spark plug can beprevented.

In this case, the control part may be configured to change the minimumvalue of the time period on the basis of the temperature of the sparkgeneration part in consideration of the fact that the fuel adheringamount corresponds to the first amount under a state where thetemperature of the spark generation part corresponds to the firsttemperature while the fuel adhering amount corresponds to the secondamount under a state where the temperature of the spark generation partcorresponds to the second temperature.

Thereby, as the temperature of the spark generation part lowers (thatis, as the amount of the fuel adhering to the spark generation partincreases), the minimum value of the interval with respect to thepre-injection increases. As a result, the increased strength of the sacchamber fuel flow can be avoided when the preceding injection is carriedout and thus, the adhering of the excessive large amount of the fuel tothe spark generation part can be prevented. Therefore, the fastincreasing of the degree of the smolder of the spark plug can beprevented.

Further, in this case, the control part may be configured to acquire thetemperature of the spark generation part on the basis of the coolingwater temperature (the temperature of the cooling water of the engine).As described above, this is because the cooling water temperature has astrong correlation with the temperature of the engine and thus, thecooling water temperature also has a strong correlation with thetemperature of the spark generation part of the spark plug.

Further, the control part may be configured to:

acquire the first parameter expressing the degree of the smolder of thespark generation part; and

change the minimum value of the time period such that the minimum valueof the time period increases as the degree of the smolder expressed bythe acquired first parameter increases.

Thereby, the minimum value of the time period is changed such that theminimum value of the time period increases as the degree of the smolderof the spark plug expressed by the first parameter increases. Therefore,as the degree of the smolder of the spark plug increases, the maximumdegree of the spread of the fuel spray can be decreased and thus, theamount of the fuel adhering to the spark generation part can be reducedand the fast increasing of the smolder of the spark generation part canbe prevented.

The other objects, features and accompanying advantages of the inventioncan be easily understood from the description of each embodiment of theinvention described below with reference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial schematic longitudinal sectional view of one ofcylinders of an internal combustion engine which the control device(first device) according to the first embodiment of the invention isapplied to.

FIGS. 2(A) and 2(B) are plan views showing shapes of the sprays of theinjected fuel in the cylinder (the combustion chamber) shown in FIG. 1,respectively.

FIG. 3 is a schematic longitudinal sectional view of the injector shownin FIG. 1.

FIG. 4 is a front view of the tip end part of the injector shown in FIG.1.

FIG. 5(A) to 5(C) are partial sectional views showing the tip end pat ofthe injector shown in FIG. 1 along a plane including the center axis ofthe injector, respectively

FIG. 6 is a time chart showing the lift amount of the valve body (theneedle valve) of the injector shown in FIG. 1 and the injector actuationsignal.

FIG. 7 is a block diagram of the electronic control unit of the firstdevice.

FIG. 8(A) is a view showing a timing of each of the fuel injections andFIG. 8(B) is a time chart showing changes of the needle lift amounts inthe preceding injection and the pre-injection.

FIG. 9 is a flow chart showing a routine executed by the CPU of theelectronic control unit shown in FIG. 7.

FIG. 10 is a lookup table referred by the CPU according to the firstmodification of the first device.

FIG. 11 is a flow chart showing a routine executed by the CPU of thecontrol device (the second device) according to the second embodiment ofthe invention.

FIG. 12 is a lookup table referred by the CPU according to the firstmodification of the second device,

FIG. 13 is a flow chart showing a routine executed by the CPU of thecontrol device (the third device) according to the third embodiment ofthe invention.

DESCRIPTION OF EMBODIMENTS

Below, the control device for the internal combustion engine accordingto each of the embodiments of the invention will be described withreference to the drawings. Hereinafter, the control device may bereferred to as “the present control device”.

First Embodiment <Configuration>

The control device according to the first embodiment of the invention isapplied to the internal combustion engine 10 shown in FIG. 1.Hereinafter, the control device according to the first embodiment willbe referred to as “the first device. The engine 10 is apiston-reciprocating cylinder-injection (direct-injection)spark-ignition type of the multi-cylinder (in this embodiment,four-cylinder) gasoline engine. The engine 10 has combustion chambers(cylinders) CC.

Each of the combustion chambers CC has a generally cylindrical spacedefined by the cylinder bore wall face (the side wall face of thecylinder) 11, the cylinder head bottom wall face (the combustion chamberupper wall face) 12, the top wall face 13 of the piston, and the intakeand exhaust valves 16 and 17 described below.

Intake and exhaust ports 14 and 15 are formed in the cylinder head part.The ports 14 and 15 communicates with the corresponding combustionchamber CC, respectively. Further, the intake and exhaust valves 16 and17 are provided in the cylinder head part. The intake valve 16 isconfigured to open and close the connection part between thecorresponding intake port 14 and the corresponding combustion chamber CCby a cam of an intake cam shaft not shown. The exhaust valve 17 isconfigured to open and close the connection part between thecorresponding exhaust port 15 and the corresponding combustion chamberCC by a cam of an exhaust cam shall not shown. Therefore, the combustionchamber CC is configured to be opened and closed by the correspondingintake and exhaust valves 16 and 17.

Actually, a pair of the intake ports 14 are formed corresponding to onecombustion chamber CC. The connection part between each of the intakeports 14 and the corresponding combustion chamber CC is opened andclosed by each of the corresponding intake valves 16 of a pair.Similarly, a pair of the exhaust ports 15 are formed corresponding toone combustion chamber CC. The connection part between each of theexhaust ports 15 and the corresponding combustion chamber CC is openedand closed by each of the corresponding exhaust valves 17 of a pair.

Further, the engine 10 has injectors (fuel injectors) 20 and ignitionplugs 30.

The injectors 20 are provided in the cylinder head part. Fuel injectionholes 21 a of each of the injector 20 expose to the interior of thecorresponding combustion chamber CC at the bottom wall face 12 of thecylinder head part at a generally central area in the correspondingcombustion chamber CC (a position adjacent to an area where the centeraxis CL of the cylinder bore passes through).

The ignition plugs 30 are provided in the cylinder head part. Each ofthe ignition plugs 30 is provided adjacent to the corresponding injector20. As shown in FIGS. 1, 2(A) and 2(B), a spark generation part (anelectrode part including central and ground electrodes) 30 a of theignition plug 30 exposes to the interior of the corresponding combustionchamber CC at the bottom wall face 12 of the cylinder head at a positionadjacent to the injection holes 21 a of the corresponding injector 20(at a generally central part of the combustion chamber CC).

As shown in FIG. 3, the injector 20 has a nozzle body part 21, a needlevalve 22 as a valve body, a coil spring 23 and a solenoid 24.

Cylindrical spaces A1 to A3 are formed in the nozzle body part 21. Thespaces A1 to A3 are formed coaxially about the center axis CN of thenozzle body part 21 and communicate with each other. As shown in FIG. 4,a plurality (in this embodiment, eight) of the injection holes 21 a areformed in the tip end part of the nozzle body part 21.

Each of the injection holes 21 a is a communication hole which connectsthe cylindrical space A1 to the exterior of the injector 20. Further, asshown in FIGS. 5(A) to 5(C), a sac chamber Sk for reserving the fuel isformed at the tip end part of the nozzle body part 21 within an areaenclosed by the injection holes 21 a. The sac chamber Sk has a generallysemisphere shape.

As shown in FIG. 4, the injection holes 21 a are formed in the tip endpart of the nozzle body part 21 such that the injection holes 21 a areequiangularly spaced apart from each other in the radially directionalong the circle about the center axis CN. Thereby, when the fuel isinjected through the injection holes 21 a, the fuel sprays Fm are formedeach having a shape shown in FIGS. 1 and 2. Each of the fuel sprays Fmhas a generally cone shape.

The spark generation part 30 a of the ignition plug 30 described aboveis positioned at a position where the fuel spray Fm including at least apart of the fuel injected from the injection hole 21 a directly reaches.In particular, as shown in FIG. 2(B), the sprays Fma and Fmb are formedby the fuel injected toward the spark generation part 30 a from twoinjection holes 21 a adjacent to each other. The spark generation part30 a is located between the sprays Fma and Fmb such that a part of thesprays Fma and Fmb can reach the spark generation part 30 a. In otherwords, the spark plug 30 and the injector 20 are positioned andconfigured such that the spark generation part 30 a are located betweenthe fuel sprays Fma and Fmb formed by the fuel injected from the twoinjection holes 21 a adjacent to each other, respectively. As describedabove, the fuel is guided to the spark generation part 30 a by theinjection (the fuel spray) by the injector 20 and thus, the engine 10 isreferred to as “the spray-guided type of the engine”.

Again, referring to FIG. 3, a fuel inlet hole 21 b is formed in theproximal end part of the nozzle body part 21. The hole 21 b connects thecylindrical space A3 to a fuel delivery pipe (not shown) fluidcommunication with each other.

The needle valve 22 has a cylinder part 22 a and a jaw part 22 b. Thecylinder part 22 a has a small radius and a cylindrical shape. The jawpart 22 b has a large radius and a cylindrical shape. The cylinder part22 a has a generally semisphere shape at its tip end. The cylinder part22 a is housed in the cylindrical space A1 at the tip end side of thecylinder part 22 a. As a result, a fuel flow passage FP is formed aroundthe lip end side part of the cylinder part 22 a. In particular, the fuelflow passage FP is formed between the tip end side part of the cylinderpart 22 a and the tip end side part of the nozzle body part 21. The jaw22 b is housed in the cylindrical space A2. The needle valve 22 isconfigured to move along the central axis (the needle valve axis) CN.

Further, a fuel passage is formed in the needle valve 22. The fuelpassage connects the proximal end part of the needle valve 22 to theouter peripheral wall face of the tip end side part of the cylinder part22 a in fluid communication with each other. As a result, the fuelflowing from the fuel inlet hole 21 b into the cylindrical space A3flows in the fuel passage of the needle valve 22 and supplied to thefuel flow passage FP.

The coil spring 23 is positioned in the cylindrical space A3. The spring23 biases the needle valve 22 toward the injection holes 21 a (towardthe tip end part side of the nozzle body part 21).

The solenoid 24 is provided adjacent to the proximal end part of thenozzle body part 21 around the cylindrical space A2. The solenoid 24 isenergized by the injector actuation signal from the ECU 40 describedbelow. When the solenoid 24 is energized, the solenoid 24 generatesmagnetic force for moving the needle valve 22 toward the fuel inlet hole21 b (toward the proximal end part side of the nozzle body part 21)against the biassing force of the spring 23.

When the solenoid 24 is not energized, the tip end part of the needlevalve 22 (the tip end of the cylinder part 22 a) is pressed to the tipend part inner periphery wall face (the seat part) Sh of the nozzle bodypart 21 by the spring 23. The moving amount of the needle valve 22 alongthe center axis CN of the needle valve 22 under the state describedabove is defined as zero. Hereinafter the moving amount of the needlevalve (the valve body) 22 along the center axis CN may be referred to as“the needle lift amount” or “the lift amount”.

As shown in FIG. 5(A), when the needle lift amount is zero, theinjection holes 21 a are closed by the tip end part of the needle valve22. As a result, no fuel is supplied from the fuel flow passage FP tothe interiors of the injection holes 21 a and thus, no fuel is injected.Therefore, the seat part Sh around each of the injection holes 21 a (theedge part of each of the injection holes 21 a) configures a valve seatfor the needle valve 22.

As shown in FIGS. 5(B) and 5(C), when the solenoid 24 is energized andthereby, the needle valve 22 is moved toward the proximal end part ofthe nozzle body part 21 and the needle lift amount becomes larger thanzero, the lip end part of the needle valve 22 moves apart from the seatpart Sh. As a result, the injection holes 21 a are opened and thus, thefuel flows from the fuel passage FP into the injection holes 21 a andthen, the fuel is injected via the injection holes 21 a, respectively

When the needle lift amount becomes a predetermined amount, the jaw part22 b shown in FIG. 3 abuts the wall part which forms the cylindricalspace A2 of the nozzle body part 21. As a result, the movement of theneedle valve 22 is restricted. The needle lift amount under this stateis referred to as “the maximum lift amount or “the ball lift amount”.That is, the needle lift amount changes between zero and the maximumlift amount.

The fuel injection under a state where the maximum value of the liftamount of the needle lift amount in the fuel injection reaches themaximum lift amount shown in FIG. 5(C) is referred to as “the full liftinjection”. On the other hand, the fuel injection under a state wherethe maximum value of the needle lift amount in the fuel injection issmaller than the maximum lift amount as shown in FIG. 5(B) is referredto as “the partial lift injection”. Below, the lift amount between zeroand the maximum lift amount may be referred to as “the partial liftamount”.

The needle lift amount is controlled by changing the energization timeperiod with respect to the solenoid 24. In other words, the start timingof the fuel injection, the end timing of the fuel injection and themaximum value of the needle lift amount in the fuel injection arecontrolled on the basis of the timing of energizing the solenoid 24,etc.

For example, when a first amount shown in FIG. 6 is set as the maximumvalue of the needle lift amount in the fuel injection, the injection(the partial lift injection) is carried out as described below. That is,when the injector actuation signal is changed from zero to apredetermined voltage VInj at the timing t1, the valve body 22 starts tomove. Then, the lift amount of the valve body 22 reaches a first liftamount smaller than the maximum lift amount at the timing t2. At thistiming t2, the injector actuation signal is changed from thepredetermined voltage VInj to zero. The first device memorizes therelationship between the lift amount and the time period between thetimings t1 and t2 in the ROM (the same applies hereinafter). That is,the first device manages the injector actuation signal in terms of thetime. As a result, as shown by the dashed line PLInj1, the needle liftamount decreases from the first lift amount and then, reaches zeroimmediately after the timing t2. The fuel is injected between the timingt1 and the timing immediately after the timing t2 (substantially,between the timings t1 and t2). In this case, the amount of the injectedfuel corresponds to a value having a correlation with the area (thetriangle area) enclosed by the wave line of the needle lift amount shownin FIG. 6. Actually,the valve body 22 starts to move at the timing whenan ineffective injection time period td elapses after the timing ofchanging the injector actuation signal from zero to the predeterminedvoltage VInj. However, the ineffective injection time period td isextremely short and thus, the period td will be omitted in the followingdescription.

Similarly, when the injector actuation signal is changed to thepredetermined voltage VInj at the timing t1 and then, the injectoractuation signal is changed to zero at the timing t3 after the timingt2, the partial lift injection under a state that a second lift amountis set as the maximum value of the needle lift amount, is carried out(refer to the two-dot chain line PLInj2). In this case, the fuel isinjected between the timing t1 and the timing immediately after thetiming t3 (substantially, between the timings t1 and t3).

As shown in the broken line PLInj2′, the first device can carry out thefuel injection under a state where the maximum value of the needle liftamount is maintained at a constant value (a constant partial liftamount) for a predetermined time period. In this case, the first devicecontrols the injector actuation signal such that the injector actuationsignal alternates between the predetermined voltage VInj and zero at anextremely short cycle with a predetermined duty ratio after the timing(the timing t3) when the needle lift amount reaches the target maximumvalue or after the timing immediately before the needle lift amountreaches the target maximum value. That is, the first device balances themagnetic force generated by the solenoid 24 with the biassing force ofthe spring 23. Then, when a predetermined time period elapses (at thetiming t4′), the injector actuation signal is changed to zero. In thiscase, the fuel is injected between the timing t1 and the timingimmediately after the timing t4′ (substantially, between the timings t1and t4′).

The full lift injection is carried out as described below. That is, asshown in FIG. 6, when the injector actuation signal is changed from zeroto a predetermined voltage VInj at the timing t1, the valve body 22starts to move. Then, the lift amount of the valve body 22 reaches themaximum lift amount at the timing t4 and thus, the movement of the valvebody 22 is restricted. Therefore, the needle lift amount is maintainedat the maximum lift amount after the timing t4. When the injectoractuation signal is changed from the predetermined value VInj to zero atthe timing t5, the needle lift amount rapidly decreases from the maximumlift amount and then, the needle lift amount reaches zero at the timingt6. The fuel is injected between the timings t1 and t6 (substantially,between the timings t1 and t5).

As shown in FIG. 5(B), as the maximum value of the needle lift amount inthe fuel injection decreases, the fluid flow area between the tip endpart of the needle valve 22 and the seat part Sh decrases. Therefore,the pressure of the fuel reaching the injection holes 21 a from the fuelpassage FP lowers. Further, the turbulence occurs in the fuel flowinginto the sac chamber Sk and the injection holes 21 a As a result, thedegree of the spread of the fuel spray in the combustion chamber CCformed by the partial lift injection (the degree of the disperse of thefuel spray or the fuel spray angle θ) increases. Further, as the maximumvalue of the needle lift amount decreases even in the partial liftinjection, the degree of the spread of the fuel spray increases.Thereby; as the maximum value of the needle lift amount in the fuelinjection decreases, the amount of the fuel (the fuel droplet) reachingthe spark generation part 30 a of the spark plug 30 increases. Thus, theamount of the fuel adhering to the spark generation part 30 a (theadhering fuel amount) increases. As described above, it can be said thatthe maximum value of the needle lift amount in the fuel injection is adisperse parameter which changes the degree of the spread of the fuelspray.

The first device includes an electronic control unit (the control part)40 shown in FIG. 7. Hereinafter, the electronic control unit 40 isexpressed as “the ECU 40”. The ECU 40 is an electronic circuit deviceincluding a well-known microcomputer having the CPU, the ROM formemorizing the instructions (the programs), the lookup tables, etc., theRAM, the backup RAM, the interface, etc. The ECU 40 receives detectionsignals from sensors described below.

An air flow meter 41 (an air flow meter incorporating an intake airtemperature sensor) for detecting an intake air amount (an air mass flowrate) which is an amount (a mass flow rate) of the air suctioned intothe combustion chamber CC of the engine 10 and the intake temperatureTHA which is a temperature of the air suctioned into the combustionchamber CC.

A crank angle sensor 42 for generating a pulse every the crank shaft notshown rotates by a predetermined angle width.

A cam position sensor 43 for generating a pulse every the cam shaft notshown rotates by a predetermined angle width.

An acceleration pedal manipulation amount sensor 44 for detecting themanipulation amount AP of the acceleration pedal not shown.

A throttle valve opening degree sensor 45 for detecting the openingdegree TA of the throttle valve not shown.

A fuel pressure sensor 46 which is provided in the delivery pipe (thefuel delivery pipe) for supplying the fuel to the injectors 20 anddetects the fuel pressure Pf in the delivery pipe.

A cooling water temperature sensor 47 for detecting the cooling watertemperature THW of the engine 10.

Applied voltage sensors 48 for measuring the voltages (the appliedvoltages) V applied by the ignition device 31 of each of the cylindersCC to the corresponding ignition plug 30.

The ECU 40 is configured to acquire the absolute crank angle CA of eachof the cylinders CC on the basis of the signals from the crank anglesensor 42 and the cam position sensor 43. Further, the ECU 40 isconfigured to acquire the engine speed NE on the basis of the signalfrom the crank angle sensor 42. Furthermore, the ECU 40 may beconfigured to receive the signal PV from an in-injector pressure sensorfor detecting the pressure in the sac chamber Sk or the fuel flowpassage FP of each of the injectors 20. In addition, the ECU 40 may beconfigured to receive the signal from a resistance detection device formeasuring the insulation resistance of each of the ignition plugs 30(the spark generation parts 30 a).

The ECU 40 is configured to send the actuation signals to actuatorsdescribed below, respectively. Below, N is one of integers of 1 to 4.“#N” means Nth cylinder.

The injector 20(#N) of the Nth cylinder (#N).

The ignition device 31(#N) of the Nth cylinder (#N).

The fuel pump device 35.

Each of the ignition device 31(#N) includes an ignitor and a coil notshown. Each of the ignition device 31(#N) is configured to generate ahigh voltage on the basis of the ignition signal (the actuation signal)generated at the ignition timing SA and apply the generated high voltageto the corresponding ignition plug 30(#N) of the Nth cylinder (#N). Bythis application of the high voltage to the ignition plug 30(#N), thecorresponding spark generation part 30 a(#N) of the ignition plug 30(#N)of the Nth cylinder (#N) generates a spark for the ignition of the fuel.

The fuel pump device 35 includes a fuel pump and a fuel pressureregulation valve not shown. The fuel discharged from the fuel pump issupplied to the injectors 20(#N) via the fuel delivery pipe not shown.The ECU 40 sends the actuation signal (the instruction signal) to thefuel pressure regulation valve to change the pressure of the fuelsupplied to the injectors 20(#N).

As described above, the ECU 40 sends the injector actuation signal tothe electromagnetic mechanism of each of the injectors 20(#N). When theinjector actuation signal is zero, the solenoid 24 is not energized. Onthe other hand, when the injector actuation signal is the predeterminedvoltage VInj the solenoid 24 is energized.

<Summary of Control>

Next, the summary of the control of the first device will be described.As shown in FIG. 8(A), the first device carries out three fuelinjections described below in one combustion cycle (that is, in onecycle in each of the cylinder).

A. Intake stroke injection InjA carried out in the intake stroke.

B. Pre-injection NB carried out in the latter half of the compressionstroke.

C. Preceding injection InjC carried out after the pre-injection InjB andimmediately before the ignition timing SA.

It should be noted that the intake strok injection InjA and/or thepre-injection InjB may not be carried out when the operation state ofthe engine 10 corresponds to a predetermined state. Further, the intakestroke injection InjA may be realized by two or more fuel injectionswhen the operation state of the engine 10 corresponds to a predeterminedstate.

The intake stroke injection InjA is realized by the full lift injection.The pre-injection InjB is realized by the full lift injection (or thepartial lift injection). The preceding injection InjC is realized by thepartial lift injection.

The first device determines an amount Qc of the fuel injected by thepreceding injection InjC on the basis of parameters expressing theoperation state of the engine 10, etc. (for example, the required torqueTqreq, the engine speed NE and the intake air temperature THA).Hereinafter, the amount Qc may be referred to as “the preceding fuelinjection amount”. At the same time, the first device determines themaximum value Lc of the needle lift amount in the preceding injectionInjC shown in FIG. 8(B) on the basis of the engine speed NE.

Next, the first device estimates the temperature Tplug of the sparkgeneration part 30 a on the basis of the cooling water temperature THW0at the engine operation start and the ignition number Nc after theengine operation start. For example, the temperature Tplug is estimated(acquired) by the expression described below However, the temperatureTplug is limited to a temperature higher than or equal to the maximumtemperature Tmax. The expression is based on the fact that thetemperature Tplug of the spark generation part 30 a at the engineoperation start can be deemed to generally be equal to the cooling watertemperature THW0 and the temperature Tplug of the spark generation part30 a after the engine operation start increases as the ignition numberNc increases. The cooling water temperature THW0 in the expressiondescribed below may he the present cooling water temperature TIM.

Spark generation part temperature Tplug=THW0+a*Nc

(“a” is zero or a constant larger than zero.)

The first device determines a lower limit Llolmt of the maximum value Lcof the needle lift amount in the preceding injection InjC on the basisof the estimated (acquired) spark generation part temperature Tplug. Inparticular, as the spark generation part temperature Tplug increases,the amount of the fuel (the fuel spray) adhering to the spark generationpart 30 a decreases. In other words, as the spark generation parttemperature Tplug lowers, the amount of the fuel adhering to the sparkgeneration part 30 a at the ignition timing SA increases. Accordingly,the first device determines the lower limit Llolmt such that the degreeof the spread of the fuel spray (the degree of the disperse of the fuelspray) decreases as the estimated spark generation part temperatureTplug lowers. That is, the first device determines the lower limitLlolmt such that the lower limit Llolmt increases as the estimated sparkgeneration part temperature Tplug lowers.

As the fuel pressure Pfc at the timing of carrying out the precedinginjection InjC increases, the strength of the turbulence of the flow ofthe fuel at the border part between the fuel flow passage FP and each ofthe injection holes 21 a in the injector 20 increases. As a result, asthe fuel pressure Pfc increases, the degree of the spread of the fuelspray increases and thus, the amount of the fuel adhering to the sparkgeneration part 30 a increases even when the other conditions are thesame. In other words, as the fuel pressure Pfc increases, the amount ofthe fuel adhering to the spark generation part 30 a at the ignitiontiming SA increases. Accordingly, the first device changes (corrects)the lower limit Llolmt such that the lower limit Llolmt determined onthe basis of the spark generation part temperature Tplug increases asthe fuel pressure Pfc increases.

Further, even when the other conditions are the same, the amount of thefuel adhering to the spark generation part 30 a at the ignition timingSA increases as the fuel injection amount Qc of the preceding injectionInjC increases. Accordingly, the first device changes (corrects) thelower limit Llolmt such that the lower limit Llolmt determined on thebasis of the spark generation part temperature Tplug increases as thefuel injection amount Qc increases.

In addition, the first device acquires a first parameter P1 expressingthe degree of the smolder of the spark generation part 30 a. Inparticular the first device acquires the applied voltage (that is, theinsulation breakdown voltage of the spark generation part 30 a) Vkimmediately before the spark discharge is generated and the appliedvoltage changes rapidly as the first parameter P1 by managing thevoltage V applied to the spark generation part 30 a. In this case, thefirst parameter P1 (the insulation breakdown voltage Vk of the sparkgeneration part 30 a) decreases as the degree of the smolder of thespark generation part 30 a increases (the smolder progresses or thesmolder strengthens).

Accordingly, the first device changes the lower limit Llolmt such thatthe lower limit Llolmt increases as the degree of the smolder of thespark generation part 30 a indicated by the acquired first parameter P1increases.

Further, the first device carries out the preceding injection InjC whilelimiting the maximum value Lc of the needle lift amount to a valuelarger than or equal to the lower limit Llolmt determined as describedabove. As a result, the ignition is carried out under a state that theamount of the fuel adhering to the spark generation part 30 a isprevented from being excessively large and thus, the fast increasing ofthe degree of the smolder of the ignition plug 30 can be prevented. Itshould be noted that the first device determines the injection endtiming EOIc of the preceding injection InjC on the basis of the enginespeed NE. Then, the first device determines the fuel injection timeperiod Tc and the injection start timing SOIc of the preceding injectionInjC so as to inject the fuel injection amount Qc of the fuel by thepreceding injection InjC wider a state where the maximum value Lc islimited to the lower limit Llolmt. Then, the first device sends theinjector actuation signal corresponding to the fuel injection timeperiod and the injection start timing SOIc to the injector 20. Thesummary of the actuation of the first device was described.

<Actual Actuation of First Device>

The CPU of the ECU 40 is configured to execute a process of theignition/injection control routine shown in FIG. 9 by a flow chart foran optional cylinder every the crank angle of the optional cylindercorresponds to the intake top dead center of the optional cylinder.

Therefore, when the crank angle of a certain cylinder (a particularcylinder (#N) corresponds to the intake top dead center of theparticular cylinder, the CPU starts the process from the step 900 andexecutes the processes of the steps 905 to 955 in sequence. Then, theCPU proceeds to the step 960.

Step 905: The CPU determines the required torque (the torque required tobe output from the engine 10) Tqreq by applying the acceleration pedalmanipulation amount AP and the engine speed NE to a lookup tableMapTqreq(AP, NE). According to the table MapTqreq(AP, NE), thedetermined required torque Tqreq increases as the acceleration pedalmanipulation amount AP increases under a state where the engine speed NEis maintained at a predetermined constant engine speed.

Step 910: The CPU determines the ignition timing SA by applying therequired torque Tqreq and the engine speed NE to a lookup tableMapSA(Tqreq, NE). According to the table MapSA(Tqreq, NE), the MBT(Minimum Spark Advance For Best Torque) is set as the ignition timing SAwithin a range where no knocking occurs. It should be noted that thevarious timing including the ignition timing SA are determined as acrank angle before the compression top dead center. Therefore, as theignition timing SA increases, the ignition timing advances (refer toFIGS. 8(A) and 8(B)).

Step 915: The CPU calculates a sum Qtotal of the amounts of the fuel tobe supplied to (injected into) the particular cylinder in the combustioncycle of the particular cylinder Hereinafter, the sum Qtotal of theamounts of the fuel will be referred to as “the total injection amount”.In particular, the CPU determines the total injection amount Qtotal byapplying the required torque Tqreq and the engine speed NE to a lookuptable MapQtotal(Threq, NE). According to the table MapQtotal(Threq, NE),as the required torque Tqreq increases, the total injection amountQtotal increases under a state where the engine speed NE is maintainedat a predetermined constant engine speed.

Step 920: The CPU determines the preceding injection amount (the amountof the fuel injected by the preceding injection InjC) Qc (refer to FIG.8(B)). In particular, the CPU determines the preceding injection amountQc by applying the required torque Threq, the engine speed NE and theintake air temperature THA to a lookup table MapQc(Tqreq, NE, THA).

According to the table MapQc(Tqreq, NE, THA), the determined precedinginjection amount Qc increases as the required torque Tqreq (that is, avalue depending on the cylinder air amount suctioned into the cylinderCC in the intake stroke) increases. Further, according to the tableMapQc(Tgreq, NE, THA), the determined preceding injection amount Qcincreases as the engine speed NE decreases and the determined precedinginjection amount Qc increases as the intake air temperature THA lowers.Furthermore, the preceding injection amount Qc is set such that thepreceding injection amount Qc is about 20 percent of the total injectionamount Qtotal. It should be noted that the preceding injection amount Qcmay be determined on the basis of other parameters expressing the engineoperation state (for example, the EGR rate, the cooling watertemperature THW, etc.).

Step 925: The CPU determines a base value Lcs of the maximum value ofthe needle lift amount in the preceding injection InjC on the basis ofthe engine speed NE. In particular, the CPU determines the base valueLcs by applying the engine speed NE to a lookup table MapLcs(NE).According to the table MapLcs(NE), the determined base value Lcsdecreases as the engine speed NE decreases.

Step 930: The CPU determines the other values with respect to the fuelinjection described below as follows. It should he noted that accordingto this embodiment, the intake stroke injection InjA and thepre-injection InjB are realized by the full lift injection.

The CPU determines the injection start and end timings SQL and EOIa ofthe intake stroke injection InjA, respectively. In particular, the CPUacquires 60 to 70 percent of the total injection amount Qtotal as theintake stroke injection amount (the injection amount of the intakestroke injection InjA) Qa. The CPU determines a predetermined timingaround the 60 degrees after the intake top dead center as the injectionstart timing SOIa of the intake stroke injection InjA. The CPUcalculates the fuel injection lime period Ta of the intake strokeinjection InjA on the basis of the intake stroke injection amount Qa andthe fuel pressure Pf, converts the fuel injection time period Ta tocorresponding crank angle width CAa on the basis of the engine speed NEand determines a crank angle obtained by subtracting the correspondingcrank angle width CAa from the injection start timing SOIa as theinjection end timing EOIa of the intake stroke injection InjA(EOIa=SOIa−CAa).

The CPU determines the injection start and end tunings SOIb and EOIb ofthe pre-injection InjB, respectively. In particular, the CPU acquires avalue obtained by subtracting the intake stroke injection and precedinginjection amounts Qa and Qc from the total injection amount Qtotal asthe pre-injection amount (the injection amount of the pre-injectionInjB) Qb (Qb=Qtotal−(Q+Qc)). The CPU determines the injection starttiming SOIb of the pre-injection InjB such that the injection starttiming SOIb advances as the cooling water temperature THW lowers toavoid the excessive increasing of the amount of the fuel adhering to thetop wall face 13 of the piston. The CPU calculates the fuel injectiontime period Tb of the pre-injection InjB on the basis of thepre-injection amount Qb and the fuel pressure Pf, converts the fuelinjection time period Tb to a corresponding crank angle width CAb on thebasis of the engine speed NE and determines a crank angle obtained bysubtracting the corresponding crank angle width CAb from the injectionstart timing SOIb as the injection end timing EOIb of the pre-injectionInjB (EOIb=SOIb−CAb) (refer to FIG. 8(B)).

Step 935: The CPU determines a lower limit base value (a base value ofthe lower limit) Llmtst of the maximum value of the needle lift amountin the preceding injection InjC on the basis of the spark generationpart temperature Tplug which is estimated separately as described above.In particular, the CPU determines the lower limit base value Llmtst byapplying the spark generation part temperature Tplug to a lookup tableMapLlmtstaplug) shown in the block B1 of FIG. 9.

According to the table MapLlmtst(Tplug), the determined lower limit basevalue Llmtst decreases as the spark generation part temperature Tplugincrases (that is, as the amount of the fuel adhering to the sparkgeneration part 30 a at the ignition timing SA decreases). The lowerlimit base value Llmtst is a base value of the lower limit Llolmt of themaximum value of the needle lift amount in the preceding injection InjCcalculated at the step 955 described below. Therefore, such anacquirement of the lower limit base value Llmtst means that theincreasing of the degree of the spead of the fuel spray can bepermissible as the spark generation part temperature Tplug increases.

Step 940: The CPU estimates (acquires) the fuel pressure Pfc at thestart timing (the injection start timing SOIc) of the precedinginjection InjC on the basis of the present fuel pressure Pf, the presentintake stroke injection amount Qa and the present pre-injection amountQb. In particular, the CPU estimates the fuel pressure Pfc by applyingthe present fuel pressure Pf, the present intake stroke injection amountQa and the present pre-injection amount Qb to a lookup table MapPfc(Pf,Qa, Qb). According to the map MapPfc(Pf, Qa, Qb), the determined fuelpressure Pfc increases as the present fuel pressure Pf increases, thedetermined fuel pressure Pfc decreases as the intake strok injectionamount Qa increases and the determined fuel pressure Pfc decreases asthe pre-injection amount Qb increases.

Next, the CPU calculates a fuel pressure correction value (a correctionvalue for correcting the lower limit base value Llmtst) ΔLpfc byapplying the estimated (acquired) fuel pressure Pfc to a lookup tableMapΔLpfc(Pfc) shown in the block B2 of FIG. 9. According to the tableMapΔLpfc(Pfc), the calculated correction value ΔLpfc increases as theestimated (acquired) fuel pressure Pfc increases. It should be notedthat the correction value ΔLpfc is zero when the estimated (acquired)fuel pressure Pfc corresponds to the base pressure Pfcst.

The correction value ΔLpfc is added to the lower limit base value Llmtstto acquire the lower limit Llolmt of the maximum value of the needlelift amount at the step 955 as described below Therefore, such asacquisition of the correction value ΔLpfc means that the lower limitLlolmt increases as the fuel pressure Pfc increases.

Step 945: The CPU calculates a preceding injection amount correctionvalue (a correction value for correcting the lower limit base valueLlmtst) ΔLQc by applying the preceding injection amount Qc to a lookuptable MapΔLQc(Qc) shown in the block 133 of FIG. 9. According to thetable MapΔLQc(Qc), the calculated correction value ΔLQc increases as thepreceding injection amount Qc increases. It should be noted that thecorrection value ΔLQc is zero when the preceding injection amount Qccorresponds to the base preceding injection amount Qcst.

The correction value ΔLQc is added to the lower limit base value Llmtstto acquire the lower limit Llolmt of the maximum value of the needlelift amount at the step 955 as described below Therefore, such anacquisition of the correction value ΔLQc means that the lower limitvalue Llolmt increases as the preceding injection amount Qc increases.

Step 950: The CPU reads out the insulation breakdown voltage Vk of thespark plug 30(#N) of the particular cylinder (#N). The insulationbreakdown voltage Vk is measured (acquired) as a voltage V immediatelybefore the voltage V starts to rapidly and extremely largely oscillate(that is, the spark is generated by the spark generation part 30 a(#N))by managing the voltage V applied to the spark plug 30(#N) by the sparkdevice 31(#N) through a routine not shown. When the degree of thesmolder of the spark plug 30 increases, the insulation breakdown voltageVk lowers. Therefore, the insulation breakdown voltage Vk is a parameterexpressing the degree of the smolder of the spark plug 30. Hereinafter,for convenience, the parameter will be referred to as “the firstparameter”.

Next, the CPU calculates a plug smolder degree correction value (acorrection value for correcting the lower limit base value Llmtst) ΔLvkby applying the read out insulation breakdown voltage Vk to a lookuptable MapΔLvk(Vk) shown in the block B4 of FIG. 9. According to thetable MapΔLvk(Vk), the calculated correction value ΔLvk increases as theinsulation breakdown voltage Vk lowers (that is, as the degree of thesmolder of the spark plug 30 expressed by the first parameter increases(or the smolder of the spark plug 30 progresses or strengthens). Itshould be noted that the correction value ΔLvk is zero when theinsulation breakdown voltage Vk is larger than or equal to the baseinsulation breakdown voltage Vkth. The correction value ΔLvk is added tothe lower limit base value Llmtst to acquire the lower limit Llolmt ofthe maximum value of the needle lift amount at the step 955 as describedbelow. Therefore, such an acquisition of the correction value ΔLvk meansthat the lower limit Llolmt increases as the insulation breakdownvoltage Vk lowers.

Step 955: The CPU acquires a sum of the lower limit base value Llmtst,the fuel pressure correction value ΔLpfc, the preceding injection amountcorrection value ΔLQc and the plug smolder degree correction value ΔLvkas the lower limit Llolmt of the maximum value of the needle lift amountin the preceding injection InjC. That is, the lower limit base valueLlmtst is corrected by the correction values ΔLpfc, ΔLQc and ΔLvk. As aresult, the lower limit Llolmt increases as the spark generation parttemperature Tplug lowers, the lower limit Llolmt increases as the fuelpressure Pfe at the timing of carrying out the preceding injection injCincreases, the lower limit Llolmt increases as the preceding injectionamount Qc increases and the lower limit Llolmt increases as theinsulation breakdown voltage Vk lowers (that is, as the degree of thesmolder of the spark plug 30 increases).

Next, the CPU proceeds to the step 960 where the CPU judges if the basevalue Lcs of the maximum value of the needle lift amount in thepreceding injection InjC acquired at the step 925 is smaller than thelower limit Llolmt of the maximum value of the needle lift amount.

When the base value Lcs is smaller than the lower limit Llolmt, the CPUjudges “Yes” at the step 960 and proceeds to the step 965 Where the CPUsets the lower limit Llolmt as the maximum value Lc of the needle liftamount in the preceding injection InjC. That is, the maximum value Lc isthe lower limit Llolmt. Then, the CPU proceeds to the step 975.

On the other hand, when the base value Lcs is larger than or equal tothe lower limit Llolmt, the CPU judges “No” at the step 960 and proceedsto the spte 970 where the CPU sets the base value Lcs as the maximumvalue Lc of the needle lift amount in the preceding injection InjC. Thatis, the maximum value Lc is the base value Lcs.

Then, the CPU proceeds to the step 975 Where the CPU executes a processfor executing the ignition at the ignition timing SA, the intake strokinjection InjA, the pre-injection InjB and the preceding injection InjC,respectively.

It should be noted that the CPU determines the injection end timing EOIcof the preceding injection InjC by applying the engine speed NE, thefuel pressure Pfc and the cooling water temperature THW to a lookuptable MapEOIc(NE, Pfc, THW). Next, the CPU calculates a time period Tc(the preceding injection time period) necessary to inject the precedinginjection amount Qc of the fuel under a state where the value Lc is setas the maximum value of the needle lift amount on the basis of themaximum value Lc, the preceding injection amount Qc and the fuelpressure Pfc. Then, the CPU converts the preceding injection time periodTc to a corresponding crank angle width CAc on the basis of the enginespeed NE and determines a crank angle obtained by adding thecorresponding crank angle width CAc to the injection end timing EOIc asthe injection start timing SOIc of the preceding injection Injc(SOIc=EOIc+CAc). Then, the CPU proceeds to the step 995 where the CPUterminates the routine.

As described above, the control part (the ECU 40) of the first device isconfigured to use the maximum value Lc of the needle lift amount in thepreceding injection InjC as a disperse parameter for changing the degreeof the spread of the fuel spray (the degree of the disperse of the fuelspray) including the fuel injected by the preceding injection InjC(refer to FIGS. 5, 8(B) and 9).

Further, the control part is configured to control the disperseparameter for changing the degree of the spead of the fuel spray (thatis, the lower limit Llolmt of the maximum value Lc of the needle liftamount) such that the maximum degree of the spread of the fuel spray inthe preceding injection InjC under a state where the amount of the fueladhering to the spark generation part 30 a at the ignition timing SAcorresponds to a first amount, is smaller than the maximum degree of thespread of the fuel spray in the preceding injection InjC that under astate where the amount of the fuel adhering to the spark generation part30 a at the ignition timing SA corresponds to a second amount smallerthan the first amount (refer to the steps 925 and 935 to 970 of FIG. 9).

Furthermore, the control part is configured to change the lower limitLlolmt depending on the temperature of the spark generation part 30 a inconsideration of the fact that the adhering amount of the fuel is thefirst amount under a state where the temperature Tplug of the sparkgeneration part 30 a corresponds to a first temperature (refer to“Tplug1” in the block B1 of FIG. 9) and the adhering amount of the fuelis the second amount under a state where the temperature Tplug of thespark generation part 30 a corresponds to a second temperature higherthan the first temperature (refer to “Tplug2” in the block B1 of FIG. 9)(refer to the values Llmt1 and Llmt2 in the block B1 and the steps 935and 955 of FIG. 9).

Further, the control part is configured to change the lower limit Llolmtdepending on the fuel pressure Pfc in consideration of the fact that theadhering amount of the fuel is the first amount under a state where thefuel pressure Pfc at the timing of carrying out the preceding injectionInjC corresponds to a first pressure and the adhering amount of the fuelis the second amount under a state where the fuel pressure Pfc at thetiming of carrying out the preceding injection InjC corresponds to asecond fuel pressure lower than the first pressure (refer to the blockB2 and the steps 940 and 955 of FIG. 9).

Furthermore, the control part is configured to change the lower limitLlolmt depending on the fuel injection amount Qc of the precedinginjection InjC in consideration of the fact that the adhering amount ofthe fuel is the first amount under a state Where the fuel injectionamount Qc of the preceding injection InjC corresponds to a firstinjection amount and the adhering amount of the fuel is the secondamount under a state where the fuel injection amount Qc of the precedinginjection InjC corresponds to a second injection amount smaller than thefirst injection amount (refer to the block B3 and the steps 945 and 955of FIG. 9).

Further, the control part is configured to:

acquires the first parameter (the insulation breakdown voltage Vk)expressing the degree of the smolder of the spark generation part 30 a;and

change the lower limit Llolmt such that the lower limit Llolmt increasesas the degree of the smolder expressed by the acquired first parameterincreases (refer to the block B4 and the steps 950 and 955 of FIG. 9).

Therefore, according to the first device, when the fuel is likely toadheres to the spark generation part 30 a or when the degree of thesmolder of the spark plug 30 is large, the excessive increasing of thedegree of the spread of the fuel spray is prevented and thus, theexcessive increasing of the amount of the fuel adhering to the sparkgeneration part 30 a is prevented. As a result, the fast increasing ofthe degree of the smolder of the spark plug 30 can be prevented.

It should be noted that the first device may not correct the lower limitbase value Llmtst acquired at the step 935 of FIG. 9. That is, the lowerlimit base value Llmtst itself may be used as a conclusive lower limitvalue Llolmt.

Further, the first device may acquire a conclusive lower limit Llolmt bycorrecting the lower limit base value Llmtst acquired at the step 935 byusing one or more of the correction values such as the fuel pressurecorrection value ΔLpfc, the preceding injection amount correction valueΔLQc and the plug smolder degree correction value ΔLvk.

Furthermore, the first device may acquire the lower limit Llolmtdirectly from the fuel pressure Pfc such that the lower limit Llolmtincreases as the fuel pressure Pfc increases. Similarly, the firstdevice may acquire the lower limit Llolmt directly from the precedinginjection amount Qc such that the lower limit Llolmt increases as thepreceding injection amount Qc increases. Further, the first device mayacquire the lower limit Llolmt directly from the first parameter suchthat the lower limit Llolmt increases as the degree of the smolder ofthe spark plug 30 expressed by the first parameter (the insulationbreakdown voltage Vk) increases.

<First Modification of First Device>

The CPU may be configured to use the cooling water temperature THW asthe temperature Tplug of the spark generation part 30 a at the step 935of FIG. 9. In this case, the lower limit base value Llmtst of themaximum value Lc of the needle lift amount in the preceding injectionInjC is determined such that the lower limit base value Llmtst increases(that is, the degree of the spread of the fuel spray decreases) as thecooling water temperature THW lowers.

In particular, the CPU determines the lower limit base value Llmtst ofthe maximum value of the needle lift amount in the preceding injectionInjC on the basis of the cooling water temperature THW. That is, the CPUdetermines the lower limit base value Llmtst by applying the coolingwater temperature THW to a lookup table MapLlmtst(THW) shown in FIG. 10.

According to the table MapLlmtst (THW), the lower limit base valueLlmtst is determined such as the lower limit base value Llmtst decreasesas the cooling water temperature THW increases (that is, as the amountof the fuel adhering to the spark generation part 30 a at the ignitiontiming SA decreases).

However, when the cooling water temperature THW is used in place of thetemperature Tplug, the control of the maximum value Lc of the needlelift amount by using the lower limit Llolmt is desirably carried out atthe start of the operation of the engine 10 and/or during the severalignitions are carried out after the start of the operation of the engine10.

<Second Modification of First Device>

The CPU of the second modification of the first device employs the fuelpressure Pf acquired at a timing adjacent to the intake top dead centeras the fuel pressure Pfc at the timing of carrying out the precedinginjection InjC used at the step 940, etc. of FIG. 9 assuming that thefuel pressure Pf moderately changes such that there is almost no changeof the fuel pressure Pf during one rotation of the engine 10.

Second Embodiment

The control device of the engine according to the second embodiment ofthe invention (hereinafter, this control device may be referred to as“the second device”) is the same as the first device except that thesecond device changes the lower limit Llolmt in consideration of theinfluence of the flow of the fuel in the sac chamber Sk of the injector20 generated by the pre-injection InjB on the preceding injection InjC.Hereinafter, the flow of the fuel remaining in the sac chamber Sk of theinjector 20 at the start timing (the injection start timing SOIc) of thepreceding injection InjC may be simply referred to as “the sac chamberfuel flow”.

In particular, the flow of the fuel (the turbulence of the flow of thefuel) occurs in the sac chamber Sk of the injector 20 by thepre-injection InjB. If the preceding injection InjC is carried out undera state that the fuel flow remains in the sac chamber Sk, the spray ofthe injected fuel easily disperses (the degree of the spread of the fuelspray increases) and the penetration force weakens. Therefore, as thestrength of the sac chamber fuel flow increases, the amount of the fuel(the fuel spray) reaching the spark generation part 30 a incrases and asa result, the amount of the fuel adhering to the spark generation part30 a increases.

The strength of the sac chamber fuel flow increases as the time periodbetween the injection end timing EOIb of the pre-injection InjB and theinjection start timing SOIc of the preceding injection InjC shortened.Hereinafter, the time period will be referred to as “the interval Tintwith respect to the pre-injection InjB”. Therefore, the degree of thespread of the spray of the fuel injected by the preceding injection InjCincreases as the interval Tint with respect to the pre-injection InjBshortens.

Further, the strength of the sac chamber fuel flow increases as the fuelinjection amont Qb of the pre-injection InjB increases. Therefore, thedegree of the spread of the spray of the fuel injected by the precedinginjection InjC increases as the fuel injection amount Qb increases.

Accordingly, the second device estimates the strength Sff of the sacchamber fuel flow on the basis of the fuel injection amount Qb of thepre-injection InjB and the interval Tint with respect to thepre-injection InjB and increases the lower limit Llolmt as the strengthSff of the sac chamber fuel flow increases. As a result, the seconddevice substantially increases the lower limit Llolmt as the intervalTint with respect to the pre-injection 4B shortens and the second devicesubstantially increases the lower limit Llolmt as the fuel injectionamount Qb increases. Thereby, the ignition under a state where theamount of the fuel adhering to the spark generation part 30 a is large,is prevented and thus, the fast increasing of the degree of the smolderof the spark plug 30 can be prevented.

<Actual Actuation of Second Device>

The CPU of the second device is configured to execute a process of theignition/injection control routine shown in FIG. 11 by a flow chart foran optional cylinder every the crank angle of the optional cylindercorresponds to the intake top dead center of the optional cylinder.

Therefore, when the crank angle of a certain cylinder (a particularcylinder (#N)) corresponds to the top dead center of the particularcylinder, the CPU starts the process from the step 1100 and executes theprocesses of the steps 905 to 925 described above in sequence. Thereby,the required torque Threq, the ignition timing SA, the total injectionamount Qtotal, the preceding injection amount Qc, the base value Lcs ofthe maximum value of the needle lift amount in the preceding injectionInjC, etc. are determined.

Next, the CPU executes the process of the step 930 described above todetermine the other values with respect to the fuel injections. Thedetermined values include following values.

Injection start and end timings SOIb and EOIb of the pre-injection InjB.

Fuel injection amount Qb of the pre-injection InjB.

Injection start and end timings SOIa and EOIa of the intake strokeinjection InjA.

Fuel injection amount Qa of the intake stroke injection InjA.

Further, the CPU executes the processes of the steps 935 to 950described above in sequence. Thereby, the following values are acquired.

Lower limit base value (the base value of the lower limit) Llmtst of themaximum value of the needle lift amount in the preceding injection InjC.

Fuel pressure Pfc at the injection start timing SOIc of the precedinginjection InjC.

Fuel pressure correction value ΔLpfc (Correction value ΔLpfc forcorrecting the lower limit base value Llmtst).

Preceding injection amount correction value ΔLQc (Correction value ΔLQcfor correcting the lower limit base value Llmtst).

Plug smolder degree correction value ΔLvk (Correction value ΔLvk forcorrecting the lower limit base value Llmtst).

Next, the CPU executes the processes of the step 1110 to 1150 describedbelow in sequence and then, proceeds to the step 960.

Step 1110: The CPU determines the injection start timing SOIc of thepreceding injection InjC on the basis of the engine speed NE. That is,the CPU determines the injection start timing SOIc such that theinjection start timing SOIc advances as the engine speed NE increases.

Step 1120: The CPU acquires a crank angle width CAint between theinjection end timing EOIb of the pre-injection InjB and the injectionstart timing SOIc of the preceding injection InjC by subtracting theinjection start timing SOIc of the preceding injection InjC from theinjection end timing EOIb of the pre-injection InjB (CAint=InjC+InjB)and determines the interval Tint with respect to the pre-injection InjBon the basis of the acquired crank angle width CAint and the enginespeed NE (refer to FIG. 8(B)).

Step 1130: The CPU estimates (acquires/determines) the strength Sff ofthe sac chamber fuel flow on the basis of the fuel injection amount Qbof the pre-injection InjB and the interval Tint with respect to thepre-injection InjB. In particular, the CPU acquires the strength Sff ofthe sac chamber fuel flow by applying the fuel injection amount Qb andthe interval Tint to a lookup table MapSff(Qb, Tint). According to thetable MapSff(Qb, Tint), the strength SIT of the sac chamber fuel flowincreases as the fuel injection amount Qb increases and the strength Sffof the sac chamber fuel flow increases as the interval Tint shortens.

Step 1140: The CPU calculates the fuel flow correction value ΔLsff (thecorrection value ΔLsff for correcting the lower limit base value Llmtst)by applying the estimated (acquired) strength Sff of the sac chamberfuel flow to a lookup table MapΔLsff(Sff) shown in the block 95 of FIG.10. According to the table MapΔLsff(Sff), the calculated correctionvalue ΔLsff increases as the estimated (acquired) strength Sff of thesac chamber fuel flow increases (strengthens).

Step 1150: The CPU acquires the sum of the lower limit base valueLlmtst, the fuel pressure correction value ΔLpfc, the precedinginjection amount correction value ΔLQc, the plug smolder degreecorrection value ΔLvk and the fuel flow correction value ΔLsff as thelower limit Llolmt of the maximum value of the needle lift amount of thepreceding injection InjC (Llolmt=Llmtst+ΔLpfc+ΔLQc+ΔLvk+ΔLsff). That is,the lower limit base value Llmtst is corrected by the correction valuesΔLpfc, ΔLQc, ΔLOvk and ΔLsff. As a result, the lower limit Llolmtincreases as the temperature Tplug of the spark generation part 30 alowers. The lower limit Llolmt increases as the fuel pressure Pfc at thetiming of carrying out the preceding injection InjC increases. The lowerlimit Llolmt increases as the preceding injection amount Qc increases.The lower limit Llolmt increases as the insulation breakdown voltage Vklowers (that is, as the degree of the smolder of the spark plug 30increases). The lower limit Llolmt increases as the strength sff of thesac chamber fuel flow increases.

Next, the CPU proceeds to the step 960 where the CPU judges if the basevalue Lcs of the needle lift amount in the preceding injection InjCacquired at the foregoing step 925 is smaller than the lower limitLlolmt of the maximum value of the needle lift amount acquired at thestep 1150.

When the base value Lcs is smaller than the lower limit Llolmt, the CPUjudges “Yes” at the step 960 and proceeds to the step 965 where the CPUsets the lower limit Llolmt as the maximum value Lc of the needle liftamount in the preceding injection InjC. That is, in this case, themaximum value Lc is the lower limit Llolmt.

On the other hand, when the base value Lcs is larger than or equal tothe lower limit Llolmt, the CPU judges “No” at the step 960 and proceedsto the step 970 where the CPU sets the base value Lcs as the maximumvalue Lc of the needle lift amount in the preceding injection InjC. Thatis, in this case, the maximum value Lc is the base value Lcs.

Then, the CPU proceeds to the step 975 described above where the CPUexecutes the processes for carrying out the ignition and each of thefuel injections, respectively. It should be noted that the CPUcalculates a time period Tc (that is, the preceding injection timeperiod Tc) necessary to inject the preceding injection amount Qc of thefuel under a state where the value Lc is set as the maximum value of theneedle lift amount on the basis of the maximum value Lc, the precedinginjection amount Qc and the fuel pressure Pfc at the step 975. Then, theCPU converts the preceding injection time period Tc to a correspondingcrank angle width CAc on the basis of the engine speed NE and acquiresthe injection end timing EOIc of the preceding injection InjC bysubtracting the crank angle width CAc from the injection start timingSOIa of the intake stroke injection InjA (EOIc=SOIa−CAc). Then, the CPUproceeds to the step 995 where the CPU terminates the routine.

As described above, the control part (the ECU 40) of the second deviceis configured to use the maximum value Lc of the needle lift amount inthe preceding injection InjC as the disperse parameter similar to thefirst device (refer to FIG. 11).

Further, the control part is configured to control the disperseparameter (that is, the lower limit Llolmt of the maximum value Lc ofthe needle lift amount) for changing the degree of the spread of thefuel spray formed by the preceding injection InjC such that the maximumdegree of the spread of the fuel spray formed by the preceding injectionInjC under a state where the amount of the fuel adhering to the sparkgeneration part 30 a at the ignition timing SA corresponds to a firstamount, is smaller than the maximum degree of the spread of the fuelspray formed by the preceding injection InjC that under a state wherethe amount of the fuel adhering to the spark generation part 30 a at theignition timing SA corresponds to a second amount smaller than the firstamount (refer to the steps 925, 935 to 950, 1110 to 1150 and 960 to 970of FIG. 11).

In addition, the control part is configured to:

acquire a second parameter (Sff) having a correlation with the strengthof the sac chamber fuel flow; and

change the lower limit Llolmt such that the lower limit Llolmt increasesas the strength of the sac, chamber fuel flow expressed by the acquiredsecond parameter increases (refer to the block B5 and the step 1130,1140 and 1150 of FIG. 11).

Further, the control part is configured to acquire the second parameter(Sff) on the basis of the interval Tint with respect to thepre-injection InjB (the time period between the injection end timingEOIb of the pre-injection InjB and the injection stall timing SOIc ofthe preceding injection InjC) (refer to the step 1130 of FIG. 11).Furthermore, the control part is configured to acquire the secondparameter (Sff) on the basis of the fuel injection amount Qb of thepre-injection InjB (refer to the step 1130 of FIG. 11).

Therefore, even when the strength of the sac chamber fuel flow is large,the excessive increasing of the degree of the spread of the fuel sprayformed by the preceding injection InjC is prevented and thus, theexcessive increasing of the amount of the fuel adhering to the sparkgeneration part 30 a is prevented. As a result, the fast increasing ofthe degree of the smolder of the ignition plug 30 can be prevented.

<First Modification of Second Device>

The CPU of the first modification of the second device calculates thefuel flow correction value ΔLsff (a correction value ΔLsff forcorrecting the lower limit base value Llmtst) by applying the intervalTint with respect to the pre-injection InjB to a lookup tableMapΔLsff(Tint) shown in FIG. 12. According to the table MapΔLsff(Tint),the calculated correction value ΔLsff increases as the interval Tintwith respect to the pre-injection InjB shortens.

<Second Modification of Second Device>

The CPU of the second modification of the second device calculates thefuel flow correction value ΔLsff (a correction value ΔLsff forcorrecting the lower limit base value Llmtst) by applying the fuelinjection amount Qb of the pre-injection InjB to a lookup tableMapΔLsff(Qb) not shown. According to the table MapΔLsff(Qb), thecalculated correction value ΔLsff increases as the fuel injection amountQb increases.

Third Embodiment

The control device of the engine according to the third embodiment ofthe invention (hereinafter, this control device may be referred to as“the third device”) changes the minimum value Tmin of the interval Tintwith respect to the pre-injection InjB in consideration of the influenceof the sac chamber fuel flow on the preceding injection InjC. That is,the third device employs the interval Tint with respect to thepre-injection InjB as the disperse parameter for changing the degree ofthe spread of the fuel spray formed by the preceding injection InjC.

When the interval Tint with respect to the pre-injection InjB is limitedto the minimum value Tmin, the strength of the sac chamber fuel flowweakens as the minimum value Tmin increases. Therefore, in this case,the degree of the spread of the spray of the fuel injected by thepreceding injection InjC decrases and the amount of the fuel adhering tothe spark generation part 30 a decreases. As a result, the fastincreasing of the degree of the smolder of the spark plug 30 can beprevented.

<Actual Activation of Third Device>

The CPU of the third device is configured to execute a process of theignition/injection control routine shown in FIG. 13 by a flow chart foran optional cylinder every the crank angle of the optional cylindercorresponds to the intake top dead center of the optional cylinder.

Therefore, when the crank angle of a certain cylinder (a particularcylinder (#N)) corresponds to the intake top dead center of theparticular cylinder, the CPU starts the process from the step 1300 andexecutes the processes of the steps 905 to 920 as described above insequence. Thereby, the required torque Tqreq, the ignition timing SA,the total injection amount Qtotal and the preceding injection amount Qcare determined.

Next, the CPU proceeds to the step 1310 where the CPU determines themaximum value Lc of the needle lift amount in the preceding injectionInjC. In particular, the CPU determines the maximum value Lc of theneedle lift amount by applying the engine speed NE and the cooling watertemperature THW to a lookup table MapLc(NE, THW). According to the tableMapLc(NE, THW), the determined maximum value Lc decreases as the enginespeed NE decreases. The determined maximum value Lc decreases as thecooling water temperature THW decreases.

Next, the CPU executes the process of the step 930 described above wherethe CPU determines the other values with respect to the fuel injections.The determined other values include the injection start timing SOIb, theinjection end timing EOIb and the fuel injection amount Qb of thepre-injection InjB. Next, the CPU executes the process of the step 1110described above where the CPU determines the injection start timing SOIcof the preceding injection InjC. Then, the CPU executes the processes ofthe steps 1320 to 1350 described below in sequence and then, proceeds tothe step 1360.

Step 1320: The CPU acquires a crank angle width CAint between theinjection end timing EOIb of the pre-injection InjB and the injectionstart timing SOIc of the preceding injection InjC by subtracting theinjection start timing SOIc of the preceding injection InjC from theinjection end timing EOIb of the pre-injection InjB (CAint=EOIb−SOIc)and then, determines the interval base value Tintst (the base valueTintst of the interval Tint with respect to the pre-injection InjB) onthe basis of the acquired crank angle width CAint and the engine speedNE.

Step 1330: The CPU determines a interval minimum base value Tminst (abase value Tminst of the minimum value of the interval Tint with respectto the pre-injection InjB) on the basis of the spark generation parttemperature Tplug acquired separately as described above. In particular,the CPU determines the interval minimum base value Tminst by applyingthe spark generation part temperature Tplug to a lookup tableMapTminst(Tplug) shown in the block B6 of FIG. 13.

According to the table MapTminst(Tplug), the determined interval minimumbase value Tminst decreases (shortens) as the spark generation parttemperature Tplug increases (that is, as the amount of the fuel adheringto the spark generation part 30 a at the ignition timing SA decreases).The interval minimum base value Tminst is a base value of the minimumvalue Tmin of the interval Tint with respect to the pre-injection InjB(the time period Tint between the injection end timing EOIb of thepre-injection InjB and the injection start timing SOIc of the precedinginjection InjC) calculated at the step 1350 described below. Therefore,such an acquisition of the interval minimum base value Tminst means thatthe permissible interval Tint with respect to the pre-injection InjBdecreases (shortens) as the spark generation part temperature Tplugincreases and thus, the permissible degree of the spread of the fuelspray increases.

Step 1340: The CPU reads out the insulation breakdown voltage Vk of thespark plug 30(#N) of the particular cylinder (#N) acquired separately bya routine not shown similar to the step 950 described above. Further,the CPU calculates the correction value ΔTvk (the plug smolder degreecorrection value ΔTvk) for correcting the interval minimum base valueTminst by applying the read out insulation breakdown voltage Vk to alookup table MapΔTvk(Vk) shown in the block B7 of FIG. 13. According tothe table MapΔTvk(Vk), the calculated correction value ΔTvk increases asthe insulation breakdown voltage Vk lowers. It should be noted that thecorrection value ΔTvk is zero when the insulation breakdown voltage Vkis larger than or equal to the base insulation breakdown voltage Vkth.

Step 1350: The CPU acquires a value obtained by adding the plug smolderdegree correction value ΔTvk to the interval minimum base value Tminstas the minimum value Tmin of the interval Tint with respect to thepre-injection InjB (Tmin=Tminst+ΔTvk). That is, the interval minimumbase value Tminst is corrected by the plug smolder degree correctionvalue ΔTvk. As a result, the minimum value Tmin increases as the sparkgeneration part temperature Tplug lowers. Further, the minimum valueTmin increases as the insulation breakdown voltage Vk lowers (that is,as the degree of the smolder of the spark plug 30 increases).

Next, the CPU proceeds to the step 1360 where the CPU judges if theinterval base value Tintst acquired at the foregoing step 1320 issmaller than the minimum value Tmin acquired at the foregoing step 1350.

When the base value Tintst is smaller than the minimum value Tmin, theCPU judges “Yes” at the step 1360 and then, proceeds to the step 1370where the CPU set the minimum value Tmin as the interval Tint withrespect to the pre-injection InjB. That is, in this case, the intervalTint with respect to the pre-injection InjB is the minimum value Tmin.

Next, the CPU proceeds to the step 1380 where the CPU corrects theinjection end and start timings EOIb and SOIb of the pre-injection InjBon the basis of the interval Tint determined at the step 1370. That is,the CPU converts the interval Tint with respect to the pre-injectionInjB determined at the step 1370 to a corresponding crank angle widthCAint on the basis of the engine speed NE and then, the CPU acquires avalue by adding the crank angle width CAint to the injection starttiming SOIc acquired at the step 1110 as a new (conclusive) injectionend timing EOIb of the pre-injection InjB (EOIb=SOIc+CAint). Further,the CPU converts the fuel injection time period Tb to a correspondingcrank angle width CAb on the basis of the engine speed NE and then,determines a crank angle obtained by adding the crank angle width CAb tothe injection end timing EOIb as the injection start timing SOIb of thepre-injection InjB (SOIs=EOIb+CAb). Then, the CPU proceeds to the step975.

On the other hand, when the base value Tintst is larger than or equal tothe minimum value Tmin, the CPU judges “No” at the step 1360 and then,proceeds to the step 1390 where the CPU sets the base value Tintst asthe interval Tint with respect to the pre-injection InjB. That is, inthis case, the interval Tint with respect to the pre-injection InjB isthe base value Tintst. Then, the CPU proceeds to the step 975.

At the step 975, the CPU executes the processes for carrying out theignition at the ignition timing SA the intake stroke injection InjA, thepre-injection InjB and the preceding injection InjC, respectively.

As described above, the control part (the ECU 40) of the third device isconfigured to use the interval Tint with respect to the pre-injectionInjB (the time period Tint between the injection end timing EOIb of thepre-injection InjB and the injection start timing SOIc of the precedinginjection InjC) as the disperse parameter (refer to FIG. 13).

Further the control part is configured to change the minimum value Tminof the interval Tint on the basis of the temperature Tplug of the sparkgeneration part 30 a in consideration of the fact that the adheringamount of the fuel is the first amount under a state where thetemperature Tplug of the spark generation part 30 a corresponds to afirst temperature (refer to “Tplug1” in the block B6 of FIG. 13) and theadhering amount of the fuel is the second amount under a state where thetemperature Tplug of the spark generation part 30 a corresponds to asecond temperature higher than the first temperature (refer to “Tplug2”in the block B6) (refer to the values TMin1 and Tmin2 in the block B6and the steps 1330 and 1350 of FIG. 13).

Further, the control part is configured to:

acquire a first parameter (the insulation breakdown voltage Vk)expressing the degree of the smolder of the spark generation part 30 a;and

change the minimum value Tmin such that the minimum value Tmin increasesas the degree of the smolder of the spark plug expressed by the acquiredfirst parameter increases (refer to the bloke B7 and the steps 1340 and1350 of FIG. 13).

Therefore, the sac chamber fuel flow is weakened when the strength ofthe sac chamber fuel flow is excessively large compared with theeasiness of the adhering of the fuel to the spark generation part 30 aand/or the degree of the smolder of the spark generation part 30 a.Thereby, the excessive increasing of the degree of the spread of thefuel spray formed by the preceding injection InjC is prevented and thus,the excessive increasing of the amount of the fuel adhering to the sparkgeneration part 30 a is prevented. As a result, the fast increasing ofthe degree of the smolder of the ignition plug 30 can be prevented.

It should be noted that the third device may use the minimum value Tminwithout correcting the interval minimum base value Tminst acquired atthe step 1330.

As described above, according to the devices of the embodiments andmodifications of the invention, the preceding injection InjC can becarried out while the excessive increasing of the amount of the fueladhering to the spark generation part 30 a is prevented. As a result,the fast increasing of the degree of the smolder of the ignition plug 30can be prevented.

The invention is not limited to the embodiments described above and thevarious modifications can be employed within the scope of the invention.For example, the present control device may acquire the temperatureTplug of the spark generation part 30 a as described below

The present control device acquires the cooling water temperature THW atthe engine operation start as the engine operation start cooling watertemperature THWs.

The present control device estimates an amount of the heat generated bythe engine 10 per one cycle on the basis of the required torque Threqand estimates the increase value of the temperature of the sparkgeneration part 30 a (or the temperature in the combustion chamber CC)per one cycle on the basis of the estimated amount of the heat.

The present control device acquires a value by adding the integrationvalue of the estimated increase values of the temperature to the engineoperation start cooling water temperature THWs as the temperature Tplugof the spark generation part 30 a.

The present control device may acquire the strength Sff of the sacchamber fuel flow as described below

The present control device acquires the fuel pressure in the sac chamberSk during the time period (the interval time period) between theinjection end timing EOIb of the pre-injection InjB and the injectionstart timing SOIc of the preceding injection InjC on the basis of theoutput value of a pressure sensor including a piezo element provided inthe sac chamber Sk every a predetermined time period elapses.

The present control device acquires a value expressing the change of thefuel pressure in the sac chamber Sk during the interval time period (forexample, an average of the amplitude of the change of the fuel pressureduring the interval time period) on the basis of the acquired data andthen, acquires the strength Sff of the sac chamber fuel flow on thebasis of the acquired value expressing the change of the fuel pressurein the sac chamber Sk. In this case, as the change (the amplitude of thechange) increases, the acquired strength SIT of the sac chamber fuelflow increases.

It should be noted that the present control device may detect thepressure of the fuel upstream of the abutting part (that is, the valveseating part) between the valve body (the needle valve 22) and the edgepart of each of the injection holes 21 a in the fuel injector 20 duringthe interval dine period and acquire the strength Sff of the sac chamberfuel flow on the basis of the value expressing the change of thedetected fuel pressure during the interval time period.

The present control device may have a measurement device for measuringthe insulation resistance of the spark generation part 30 a and use theinsulation resistance measured by the measurement device as the firstparameter expressing the degree of the smolder of the spark generationpart 30 a. In this case, the determined first parameter indicates thatthe degree of the smolder of the spark generation part 30 a increases asthe insulation resistance decreases.

As described above, the first and second devices acquire the lower limitLlolmt by adding the sum of the correction values ΔLpfc, ΔLQc, ΔLvk,etc, to the lower limit base value Llmtst. On the other hand, thepresent control device may acquire correction coefficients kLpk, kLQc,kLvk and kLsff in place of the correction values ΔLpfc, ΔLQc, ΔLvk andΔLsff and then, acquire the lower limit Llolmt by multiplying the lowerlimit base value Llmtst by the correction coefficients kLpfc, kLQc, kLvkand kLsff.

Further, the injector 20 is a type of an injector in which its injectionholes 21 a are closed directly by the tip end part of the needle valve22. However, the injector 20 may be a type of an injector in which theinjection holes 21 a are formed to always communicate with therelatively large sac chamber and the needle valve 22 moves to open andclose the connection part between the sac chamber and the fuel flowpassage FP (the internal valve type of the injector).

Further, the present control device may change the degree of the spreadof the fuel spray formed by the preceding injection InjC by using theboth of the maximum value Lc of the needle lift amount in the precedinginjection InjC and the interval Tint with respect to the pre-injectionInjB as the disperse parameters, respectively while limiting the maximumvalue Lc of the needle lift amount in the preceding injection InjC andthe interval Tint with respect to the pre-injection InjB to the lowerlimit Llolmt and the minimum value Tmin, respectively.

Further, the engine 10 which the present control device is applied to,may be a spray-guided type of an internal combustion engine in which theinjection holes are provided at the border between the cylinder bore andthe cylinder head and the fuel is injected toward the central part ofthe combustion chamber CC (that is, the spark generation part 30 a).

Further, in the present control device, the maximum value Lc and thelower limit Llolmt of the needle lift amount in the preceding injectionInjC corresponds to each other at all times. That is, for example, thepresent control device may acquire the maximum value Lc which increasesas the spark generation part temperature Tplug lowers and carry out thepreceding injection InjC by using the acquired maximum value Lc.

1. A control device applied to a cylinder injection type of an internalcombustion engine, comprising: at least one cylinder; an ignition plughaving a spark generation part; and an injector having a movable valveand at least one injection hole, said injector injecting a fuel intosaid cylinder via said injection hole by a movement of said movablevalve body such that the fuel spray including at least part of the fuelinjected by said injector reaching directly said spark generation part,the control device comprising a control part configured to make saidinjector inject the fuel and make said spark generation part generate aspark for an ignition of the fuel at a predetermined ignition timing,wherein said control part is configured to control a disperse parameterfor changing a degree of a spread of the fuel spray such that themaximum degree of the spread of the fuel spray under a state where anamount of the fuel adhering to said spark generation part at theignition timing corresponds to a first amount, is smaller than themaximum degree of the spread of the fuel spray under a state where theamount of the fuel adhering to said spark generation part at theignition timing corresponds to a second amount smaller than said firstamount.
 2. The control device for the engine of claim 1, wherein saidcontrol part is configured to: use a maximum value of a lift amount ofsaid valve body in the fuel injection as said disperse parameter; anddecrease the maximum degree of the spread of the fuel spray by changinga lower limit of the maximum value of the lift amount in a precedinginjection carried out immediately before the ignition timing such thatsaid lower limit under a state where the adhering amount of the fuelcorresponds to said first amount, is larger than said lower limit undera state Where the adhering amount of the fuel corresponds to said secondamount.
 3. The control device for the engine of claim 2, wherein saidcontrol part is configured to change said lower limit on the basis ofthe temperature of said spark generation part in consideration of thefact that the adhering amount of the fuel corresponds to said firstamount under a state where the temperature of said spark generation partcorresponds to a first temperature and the adhering amount of the fuelcorresponds to said second amount under a state where the temperature ofsaid spark generation part corresponds to a second temperature higherthan said first temperature.
 4. The control device for the engine ofclaim 3, wherein said control part is configured to acquire thetemperature of said spark generation part on the basis of a temperatureof a cooling water of said engine.
 5. The control device for the engineof claim 2, wherein said control part is configured to change said lowerlimit on the basis of a fuel pressure at the timing of carrying out saidpreceding injection in consideration of the fact that the adheringamount of the fuel corresponds to said first amount under a state wherethe fuel pressure at the timing of carrying out said preceding injectioncorresponds to a first pressure and the adhering amount of the fuelcorresponds to said second amount under a state where the fuel pressureat the timing of carrying out said preceding injection corresponds to asecond pressure lower than said first pressure.
 6. The control devicefor the engine of the claim 2, wherein said control part is configuredto change said lower limit on the basis of a fuel injection amount ofsaid preceding injection in consideration of the fact that the adheringamount of the fuel corresponds to said first amount under a state wherethe fuel injection amount of said preceding injection corresponds to afirst injection amount and the adhering amount of the fuel correspondsto said second amount under a state where the fuel injection amount ofsaid preceding injection corresponds to a second injection amountsmaller than said first injection amount.
 7. The control device for theengine of claim 2, wherein said control part is configured to: acquire afirst parameter expressing the degree of the smolder of said sparkgeneration part; and change said lower limit such that said lower limitincreases as the strength of the degree of the smolder expressed by saidacquired first parameter increases.
 8. The control device for the engineof claim 2, wherein said injector has a sac chamber at a tip end part ofsaid injector, said sac chamber communicating with said injection holeunder a state where at least said valve body is moved, said controldevice is configured to: execute the fuel injection in addition to saidpreceding injection by said injector as a pre-injection before saidpreceding injection; acquire a second parameter having a correlationwith the strength of a sac chamber fuel flow generated by saidpre-injection and remaining in said sac chamber at an injection starttiming of said preceding injection; and change said lower limit suchthat said lower limit increases as the strength of the sac chamber fuelflow expressed by said acquired second parameter increases.
 9. Thecontrol device for the engine of claim 8, wherein said control part isconfigured to acquire said second parameter on the basis of a timeperiod between the injection end timing of said pre-injection and theinjection start timing of said preceding injection.
 10. The controldevice for the engine of claim 8, wherein said control part isconfigured to acquire said second parameter on the basis of the fuelinjection amount of said pre-injection.
 11. The control device for theengine of claim 8, wherein said control part is configured to acquire atleast one of a pressure of the fuel in said sac chamber during a timeperiod between the injection end timing of said pre-injection and theinjection start timing of said preceding injection and a pressure of thefuel in the injector upstream of a valve seating part during a timeperiod between the injection end timing of said pre-injection and theinjection start timing of said preceding injection, said valve seatingpart corresponding to a part where said valve body abuts an edge portionof said injection hole; and to acquire said second parameter on thebasis of a change of said acquired pressure of the fuel.
 12. The controldevice for the engine of claim 1, wherein said injector has a sacchamber at a tip end part of said injector, said sac chambercommunicating with said injection hole under a state where at least saidvalve body is moved, said control part is configured to: execute a fuelinjection in addition to said preceding injection by said injector as apre-injection before said preceding injection; use a time period betweenthe injection end timing of said pre-injection and the injection starttiming of said preceding injection as said disperse parameter; anddecrease the maximum degree of the spread of the fuel spray by changinga minimum value of said time period such that said minimum value of saidtime period under a state where the adhering amount of the fuelcorresponds to said first amount, is larger than said minimum value ofsaid time period under a state where the adhering amount of the fuelcorresponds to said second amount.
 13. The control device for the engineof claim 12, wherein said control part is configured to change saidminimum value of said time period on the basis of the temperature ofsaid spark generation part in consideration of the fact that theadhering amount of the fuel corresponds to said first amount under astate Where the temperature of said spark generation part corresponds toa first temperature and the adhering amount of the fuel corresponds tosaid second amount under a state where the temperature of said sparkgeneration part corresponds to a second temperature higher than saidfirst temperature.
 14. The control device for the engine of claim 13,wherein said control part is configured to acquire the temperature ofsaid spark generation part on the basis of a temperature of a coolingwater of said engine.
 15. The control device for the engine of claim 13,wherein said control part is configured to: acquire a first parameterexpressing the degree of the smolder of said spark generation part; andchange said minimum value of said time period such that said minimumvalue of said time period increases as the degree of the smolderexpressed by said acquired first parameter increases.